Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![OXIDE OF ZINC. and on boiling it part of the oxide of zinc separates immediately; on boiling the diluted solution, all the oxide of zinc precipitates. Ammonia salts intei-feve more oi- less with these precipitations. 8. Carbonate of soda produces a precipitate of basic carbonate of zinc, which is insoluble in an excess of the precipitant. The com- position of the precipitate varies with the degree of concentration of the solution, the temperature, and the pi'oportion of the precipitant em- ployed. The presence of salts of ammonia in great excess prevents the formation of this precipitate. 9. Carbonate of ammonia also produces the same precipitate of basic carbonate of zinc as carbonate of soda does; but this precipi- tate redissolves on adding excess of the precipitant: on boiling the dilute solution, a white precipitate is formed; ammonia salts interfere more or less with this precipitation. N.B.—Non-volatile organic acids interfere more or less with the precipitation of solutions of zinc by the caustic and carbonated alkalies. Sugar does not prevent the precipitations. 10. Carbonate of baryta does not precipitate solutions of salts of zinc in the cold, with the exception of the sulphate. 11. Ferrocyanide of potassium throws down ferrocyanide of zinc, ZugCfy [Zn„Fe(CN)5], as a white slimy precipitate, somewhat soluble in excess of the precipitant, insoluble in hydrochloric acid. 12. Ferrioyanide of potassium throws down ferricyanide of zinc, ZUgCfdy [Zn3Fe2(CN),2], as a brownish orange-yellow precipitate, soluble in hydrochloric acid and in ammonia. 13. If a mixture of oxide of zinc or one of its salts with carbonate of soda is exposed to the reducing flame of the blowpipe, the charcoal support becomes covered with a slight coating ofoxideofzinc, which is yellow while hot, but turns white on cooling ; this coating is produced by the reduced metallic zinc volatilizing at the moment of its reduction, and being reoxidized in passing through the outer flame. The metallic incrustation obtained according to p. 25 is black with a brown edge, the incrustation of oxide is white, and therefore invisible upon porcelain. It may be dissolved in nitric acid and examined accord- ing to 14. 14. If oxide of zinc or a zinc salt is moistened with solution of nitrate of cobalt, and then heated before the blowpipe, an unfused mass is obtained of a beautiful green colour; this mass is a compound of oxide of zinc with protoxide of cobalt. If, therefore, in the first experiment described in 13 the charcoal is moistened around the little cavity with solution of cobalt and ignited, the coating appears green when cold. This test may be applied with great delicacy by mixing the solution to be tested with a very little of the cobalt solution (not enough to give a bright red colour), adding carbonate of soda in slight excess, boiling, collecting the precipitate, washing it, and igniting on platinum foil. On triturating the residue, the green colour may be distinctly and readily observed (Bloxam).](https://iiif.wellcomecollection.org/image/b21966953_0144.jp2/full/800%2C/0/default.jpg)
